How I constructed a Southwold Railway 6 wheeled Cleminson open wagon using PETG filament

I have always been fascinated by the Southwold Railway - its quirkiness and individuality as one of very few three foot narrow gauge railways in England. Their continued use of Cleminson six wheeled rolling stock is also another source of interest for me and so, when I got a 3D printer and developed skills in making my own drawings and designs, it seemed inevitable that I would produce my own 6-wheeled stock. Here's how I got on.

For this build, I also decided to experiment with using PETG filament rather than my more usual PLA. My conclusions as to how they compare are outlined in the conclusion.

 The wagon was first drawn as a kit of parts using a marvellous free online package called TinkerCAD.

The TinkerCAD design environment was developed for children to use and consequently its learning curve is quite shallow, unlike a number of other 3D drawing packages. Whilst it is not as powerful as these other programs, it is remarkable how fairly complex drawings can be made with a series of simple tools.

 For more detailed information on how to use TinkerCAD see How I drew a Southwold open wagon with TinkerCAD

Once all the parts needed had been drawn, exported, sliced and 3D printed, I set to work putting them together. The first task was to join the two parts of the wagon floor using the bridging piece - which also acts as the support for the sliding centre truck.

The bridging section was first glued to one of the floor halves ......

..... and then glued to the other, making sure the two sections of floor were properly aligned and square.

NOTE: For this build, I decided to use PETG rather than my usual PLA filament as an investigation into how they compared. See below for my conclusions.

You will notice that the pivots for the outer swivelling trucks differ slightly. The one on the left with the raised edge keeps the truck level as it pivots whilst the one on the right is flat and 1.5mm lower. This is to allow for some compensation of the right hand truck as it pivots.

Next, one of the end pieces was attached. To ensure it was perpendicular to the floor, a square was used while the solvent hardened.

The floor was positioned along the lowermost plank division line on the inside of the end.

This process was repeated for the other end piece.

The sides were then added.

To enable them to fit on the print-bed, these come as two sections - long .......

..... and a short.

They were glued together when they were joined to the floor - the division between the two sections coinciding with the joint between the opening doors.

I have also produced two variants on the design the match those found on the originals. One variant has no centre straps on the doors, .....

.... whilst the other variant has the coal merchant's name, MOY, in slightly raised lettering.

The second side was then glued on and the body left to harden off. 

NOTE: For PETG, I have to use a plastic solvent (I use Plastic Weld) which takes a couple of hours to harden whereas for PLA, the thick superglue sets within a couple of minutes.

To hide the joint between the two parts of the wagon sides on the solebar, a couple of filler pieces were glued on; .......

..... one on each side.

 I next turned my attention to the three trucks. The W-irons were glued to the cross-members.

NOTE: Before glueing on the W-irons, it may be necessary to to open out the holes for the axles to 3.5mm with a drill. This will depend on how cleanly your printer produces the parts.

One of the outer trucks then had two 1.5mm strips glued along its centre line to give it a very simple (but effective) form of compensation when mounted on the flat pivot.

At this stage, I test-fitted the Bachmann 21.5mm diameter wheelsets to ensure they ran smoothly in the bearing holes.

NOTE: I don't generally use brass bushes as bearings in the holes. Maybe my wagons don't get sufficient usage, but I haven't experienced excessive wear or binding over the years.

The trucks were left overnight for the solvent to harden before moving on to the next stage.

The centre truck brackets were cleaned up (PETG tends to produce a lot of strands and whiskers as it prints) .......

.... as were the holes into which they will be inserted.

Two brackets were then glued into place .....

..... and the centre truck positioned between them.

The other two brackets were then glued on.

NOTE: Since taking these photos, I have redesigned the brackets with larger flanges to more reliably hold the truck in place.

The outer trucks were then attached to their respective mounts (the compensated truck on the flat mount) with self-tapping screws.

The trucks were then tested to ensure they slid and pivoted smoothly.

The wagon was then tested on the track.

It was then given a couple of coats of Halford's grey primer from a rattle can aerosol and then given some light weathering. Buffers and my own design of hook and loop couplings were added and the wagon entered service.

NOTE: These photos are of the centre strap-free variant

 

PETG v PLA - My conclusions

As mentioned above, I decided to explore the possibilities of using PETG for this build to see how it compares with my more usual PLA filament. Firstly, I had heard accounts from some fellow modellers that PLA has a tendency to warp when exposed to hot sunshine and secondly I was slightly anxious about the biodegradability of PLA when being used in an outdoor environment.

Here are my conclusions

• PETG prints at a higher temperature than PLA and so will probably be less susceptible to the effects of hot sunshine
• PETG is a lot more tacky and so sticks to the print bed without any problem. Following advice, I coated my glass print bed with Pritt adhesive - not to improve adhesion but actually to help with removal of the parts after printing. Unlike PLA, one coating of Pritt lasts ages.
• PETG tends to string more readily than PLA and so doesn't require as much cooling (which exacerbates stringing). I set my fan to 25% - some recommend not using cooling at all
• The print temperature is more critical for PETG than for PLA. Too hot and stringing increases, too cool and the layers don't adhere. I'm not sure I yet have the temperature perfected as a lot of the surface detail on the parts (eg bolt and rivet heads) is being lost. I may need to tweak the temperature to improve this.
• I struggled to find a solvent which worked with PETG. Superglue didn't work, Pipe Weld adhesive was unreliable for small parts. Eventually, I discovered Plastic Weld was OK - but inhaling its fumes need to be avoided. A disadvantage of using Plastic Weld is that it takes far longer to harden off than the superglue I use for PLA and so construction time is extended to days rather than hours.
  
• I haven't experienced any issues with painting PETG as yet - but my experience is limited to only a couple of models.

Overall, at this stage, I don't think any advantages of PETG outweigh those of PLA - at least in the climate of Northwest England. I doubt the sun's temperatures will be so excessive that printed parts will suffer unduly and reading further suggests that PLA biodegrades very slowly (40 years when buried in a landfill site). 

Once this reel of PETG has been exhausted, unless I have a major breakthrough with solving the problems of stringing and gluing, I will probably revert to PLA

Download

The files are available for download (in 15mm scale) from the GardenRails.org forum. The files are free to download but a log-in is required and voluntary contributions towards the upkeep of the forum are always welcome (our accounts are published on the forum).

• Download link - https://gardenrails.org/forum/viewtopic.php?f=55&t=14098

Note: There are three variants of the wagon available.

1. As shown above
2. As above but with MOY (the local coal merchant) on the sides
3. Similar to #1 but with additional strapping in the middle of each door